Fuel_cell.pdf

8/10/2019 Fuel_cell.pdf

1/23

Fuel cellFuel cell


2/23

AA fuel cellfuel cell is anis an electrochemicalelectrochemical conversionconversiondevice can convert the chemical energy of thedevice can convert the chemical energy of thefuels directly to electricity.fuels directly to electricity.

It produces electricity fromIt produces electricity from fuelfuel (on the(on the anodeanodeside) and anside) and an oxidantoxidant (on the(on the cathodecathode side),side),which react in the presence of anwhich react in the presence of an electrolyteelectrolyte..

The reactants flow into the cell, and theThe reactants flow into the cell, and thereaction products flow out of it, while thereaction products flow out of it, while theelectrolyte remains within it.electrolyte remains within it.

Fuel cells can operate continuously as long asFuel cells can operate continuously as long asthe necessary flows are maintained.the necessary flows are maintained.


3/23

Many combinations of fuel and oxidant areMany combinations of fuel and oxidant are

possible. A hydrogen cell usespossible. A hydrogen cell uses hydrogenhydrogenas fuel andas fuel and oxygenoxygen (usually from air) as(usually from air) as

oxidant.oxidant.

Other fuels includeOther fuels include hydrocarbonshydrocarbons likelike

butane, propane and methylbutane, propane and methyl alcoholalcohol..

Other oxidants includeOther oxidants include airair,, chlorinechlorine andandchlorine dioxidechlorine dioxide


4/23

Fuel Cells are classified primarily by the kind ofFuel Cells are classified primarily by the kind ofelectrolyte they employ.electrolyte they employ.

This determines the kind of chemical reactions thatThis determines the kind of chemical reactions that

take place in the cell, the kind of catalysts required, thetake place in the cell, the kind of catalysts required, thetemperature range in which the cell operates, the fueltemperature range in which the cell operates, the fuelrequired, and other factors.required, and other factors.

Types of Fuel CellsTypes of Fuel Cells

Polymer Electrolyte Membrane (PEM)Polymer Electrolyte Membrane (PEM)

AlkalineAlkaline

Phosphoric AcidPhosphoric Acid

Direct MethanolDirect Methanol

Molten CarbonateMolten Carbonate

Solid OxideSolid Oxide


5/23

The electrode (catalyst) typically comprisesThe electrode (catalyst) typically comprises

graphite impregnated with finely dividedgraphite impregnated with finely divided

platinum or a platinum group metal orplatinum or a platinum group metal orplatinumplatinum-- silver or nickel alloy.silver or nickel alloy.

The electrodes must beThe electrodes must be

1. good conductors1. good conductors

2. a good electron sources or sinks2. a good electron sources or sinks

3. not be consumed or deteriorated by3. not be consumed or deteriorated byelectrolyte heat or electrode reactionselectrolyte heat or electrode reactions


6/23

HydrogenHydrogenoxygenoxygen fuel cellfuel cellss

Based on the electrolyte:Based on the electrolyte:

Polymer Electrolyte MembranePolymer Electrolyte Membrane

(PEM)(PEM) hydrogenhydrogenoxygenoxygen fuel cellfuel cell

AlkalineAlkaline hydrogenhydrogenoxygenoxygen fuel cellfuel cell


7/23

At anodeAt anode oxidation of hydrogen take place,oxidation of hydrogen take place,which oxidise hydrogen in towhich oxidise hydrogen in to protonsprotons (H(H++))with liberation ofwith liberation of electronselectrons and forcing theand forcing the

electrons to travel though a externalelectrons to travel though a external circuitcircuit,,hence converting them to electrical power.hence converting them to electrical power.

At cathodeAt cathode, takes the electrons back in, and the, takes the electrons back in, and the

reduction of the oxidant (Oreduction of the oxidant (O22) and form oxides) and form oxidesOO22--..

OO22--combine with the protons to form Hcombine with the protons to form H22O asO as

the products (typically simple compounds likethe products (typically simple compounds likewater and carbon dioxide).water and carbon dioxide).


8/23

Alkaline HAlkaline H22--0022 fuel cellfuel cell

In the alkaline HIn the alkaline H22--0022 fuel cell:fuel cell: electrolyteelectrolyte isis

25% KOH solution.25% KOH solution.


9/23


10/23

CELL REACTIONCELL REACTION Anode: 2HAnode: 2H22+ 4OH+ 4OH

--(aq)(aq) -- 4 H4 H22O (l)O (l) + 4e+ 4e--

Cathode:Cathode:

OO22(g) + 2(g) + 2 HH22O (l)O (l) + 4e+ 4e-- -- 4 OH4 OH--((aqaq))

Net reaction:Net reaction:

2H2H22+ O+ O22(g)(g) -- 2 H2 H22O (l)O (l)

As long as there is a flow of chemicals into the cell,As long as there is a flow of chemicals into the cell,

the electricity flows out of the cell.the electricity flows out of the cell.


11/23

To deliver the desired amount of energy, the fuelTo deliver the desired amount of energy, the fuel

cells can be combined incells can be combined in series and parallelseries and parallelcircuitscircuits, where series yield higher, where series yield higher voltagevoltage, and, and

parallel allows a strongerparallel allows a stronger currentcurrent to be drawn.to be drawn.

Such a design is called aSuch a design is called afuel cell stackfuel cell stack. Further,. Further,the cell surface area can be increased, to allowthe cell surface area can be increased, to allow

strongerstronger currentcurrent from each cell.from each cell.

E cell (E cell (TheoriticalTheoritical) = 1. 23V) = 1. 23V

E cell (actual) = 0. 8E cell (actual) = 0. 81V1V


12/23

Proton exchange membrane fuelProton exchange membrane fuel

cellcell (PEMFC)(PEMFC)

A protonA proton -- conducting polymer membrane isconducting polymer membrane is

the electrolyte, which separates thethe electrolyte, which separates the anodeanode andandcathodecathode side.side.

Ex.Ex. CationCation exchange resin saturated withexchange resin saturated withwater.water.


13/23


14/23

CELL REACTIONCELL REACTION

Anode: 2HAnode: 2H22(g)(g) 4 H4 H++ + 4e+ 4e--

Cathode:Cathode:

OO22 (g) + 4 H(g) + 4 H++ + 4e+ 4e-- -- 2 H2 H22OO (aq)(aq) Net reaction:Net reaction:

2H2H22 (g) + O(g) + O22 (g)(g) --

2 H2 H22O (l)O (l)


15/23

On the anode side, hydrogen diffuses to theOn the anode side, hydrogen diffuses to theanode catalyst where it later dissociates intoanode catalyst where it later dissociates intoprotons and electrons.protons and electrons.

The protons are conducted through theThe protons are conducted through themembrane to the cathode (multimembrane to the cathode (multi--facilitatedfacilitated

proton membranes (MFPM)., but the electronsproton membranes (MFPM)., but the electronsare forced to travel in an external circuitare forced to travel in an external circuit(supplying power) because the membrane is(supplying power) because the membrane is

electrically insulating.electrically insulating.

These protons often react with oxidantsThese protons often react with oxidants


16/23

On the cathode catalyst, oxygenOn the cathode catalyst, oxygen moleculesmolecules

take the electrons (which have traveledtake the electrons (which have traveledthrough the external circuit) and combine withthrough the external circuit) and combine with

protons to form waterprotons to form water in this example, thein this example, the

only waste product, is water.only waste product, is water.

A typical PEM fuel cell produces a voltageA typical PEM fuel cell produces a voltage

from 0.8 V to 1.0 V at full rated load.from 0.8 V to 1.0 V at full rated load.


17/23

APPLICATIONSAPPLICATIONS

As auxiliary energy source in space vehicles,As auxiliary energy source in space vehicles,

submarines or militarysubmarines or military--vehiclesvehicles

The wt of 250 kg fuel battery is sufficient forThe wt of 250 kg fuel battery is sufficient for

15 days in space, but several tones of other15 days in space, but several tones of other

fuels are required for 15 daysfuels are required for 15 days

In case of HIn case of H22/O/O22 fuel cell, the product waterfuel cell, the product water

proved to be a valuable source of fresh waterproved to be a valuable source of fresh waterby the astronautsby the astronauts


18/23

HH22/O/O22 fuel cellfuel cell


19/23

The world's first certified Fuel Cell Boat (HYDRA), in Leipzig/Germany


20/23

Type 212 submarine with fuel cell propulsion of the German Navy


21/23

Toyota FCHV PEM fuel cell vehicle


22/23

A hydrogen fuel cell public bus accelerating at traffic lights in Perth,Western Australia


23/23

With a fuel cell, chemicals constantly flow intoWith a fuel cell, chemicals constantly flow into

the cell so it never goes deadthe cell so it never goes dead ---- as long as thereas long as thereis a flow of chemicals into the cell, theis a flow of chemicals into the cell, the

electricity flows out of the cell.electricity flows out of the cell.

Most fuel cells in use today use hydrogen andMost fuel cells in use today use hydrogen and

oxygen as the chemicals.oxygen as the chemicals.

Documents

Fuel_cell.pdf